It’s not the consuption it is the lack of exercise, I eat now about 4000 call a day and have been losing 2 lb a month on top of muscle gains for over a year.
The diabetes thing can be controlled with intermittent fasting… 14 hours no food intake at all. Here sometimes you get breakfast at 5 am next meal is 9 pm if things go wrong.
As for brain… use it or lose it like any other muscle.